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Re-establishing coastal wetlands

A little more than three years ago, this was shallow, open water where the marsh had subsided over time. But in 2000, the Greater Lafourche Port Commission began filling it in. The levee and the higher ground behind it were built with sediment dredged from a shipping channel, he explained.

Stopping land loss and ultimately restoring Louisiana's coastline is complicated, and researchers from the LSU AgCenter are working in coastal marshes to learn more about how to enhance the process.

"This site represents one of the techniques for restoration," he said. "It's a good example of beneficial use sediments."

The site was created by the Greater Lafourche Port Commission, which acquired about 13,000 acres to establish a mitigation area, including a wildlife sanctuary.

With a grant from the Barataria-Terrebonne National Estuary Program, the LSU AgCenter is working with the USDA’s Natural Resources Conservation Service to study how different plants survive in the various environments on the man-made island.

"Seven or eight discrete habitats on this 250-acre site provide opportunities to evaluate planting techniques, plant responses to disturbed soils – the whole dynamics across a number of different habitats," Materne said. "Our target is a functionally equivalent natural marsh."

The area is typical of the Louisiana coast, Materne said. It originally was elevated and vegetated, but the land has subsided and is now mostly under open water.

"Eighty percent of all coastal losses in the United States are in Louisiana," Materne said. "Most aren't shorelines washing away but rather land lowering, subsiding and compacting."

Louisiana's coastal wetlands were built up over time as sediments carried by the Mississippi River settled out during spring floods. For the past hundred years or so, the gradual accumulation of new land has been hindered by levees that prevent the river from spilling out into coastal areas and depositing the silt.

But building new islands won't solve the problem if waves and tides wash the soil away. That's why the LSU AgCenter and NRCS are working to find the plants that will hold the coast together and stop the wetlands loss.

Since it opened more than 15 years ago, the NRCS Plant Materials Center at Golden Meadow, La., has been selecting and collecting coastal plants that show potential for revegetating the marshes.

"We develop plants and technologies for coastal restoration efforts," said Gary Fine, manager of the Golden Meadow facility. Fine and his staff look for native vegetation and select promising plants. Then they bring the plants to the Plant Materials Center where they grow and evaluate them.

The center also provides space where marsh plants developed from LSU AgCenter research are being grown in wetlands nurseries – thanks to grant funding from USDA’s Cooperative State Research, Education and Extension Service.

Most of the plants Fine has been working with are native grasses that can be prolific in the marsh but don't reproduce very well from seed. To propagate the plants, the staff divides them into small clumps for planting. After the clumps grow larger, they're cut into small pieces and planted again to continue the process.

Once the Plant Materials Center has produced enough plants, they give starter clumps to commercial growers, who continue the increase until they've produced enough plants for transplanting in the marsh.

Materne said it takes 2,000 plants in 1-gallon containers to plant an acre of marsh. And those plants have to be transplanted by hand.

One of the first plants used in marsh restoration was Spartina alterniflora, or smooth cordgrass.

"It has a high stem density and slows down water movement - buffering the force of waves," Materne said.

Cordgrass is one of the primary marsh plants found in Louisiana, where it grows in shallow water and provides the first line of defense against erosion from waves and tides. With a high tolerance for both fresh water and salt water, it grows aggressively throughout the coastal region.

"It makes up nearly 99 percent of the vegetation in the salt marshes in Louisiana," Materne said. "It's the plant that's holding Louisiana together."

Spartina, however, doesn't produce very good seeds in the wild.

To help solve the problem, scientists at the LSU AgCenter have been applying traditional plant breeding techniques used for agricultural crops in an effort to improve seed production and plant vigor in Spartina and other marsh plants.

In 1988 and 1989 NRCS scientists collected seeds of native Spartina plants from Louisiana's coastal marshlands and planted them in Golden Meadow. Researchers have been evaluating the results in coastal marshes and nurseries since then.

LSU AgCenter scientists identified plants with improved seed set, disease resistance or plant vigor and cross-pollinated them to produce new plants that combine all of the desired traits, according to Steve Harrison, an AgCenter plant breeder who also works with wheat and oats.

"This is similar to the methods used to develop improved varieties of cultivated crops such as wheat or sugarcane, except that the final product must be genetically diverse and representative of native populations in addition to having the selected traits," Harrison said.

The researchers have been successful enough that about 35 acres of shoreline levees around the Port Fourchon site were seeded successfully with Spartina by airplane in March 2002.

With the levees protected and the area filled in, AgCenter and NRCS researchers began looking at plants for other environmental conditions.

"The area's well on its way to recovery," Materne said. "The Spartina is on the levees to protect and maintain the barrier – to stop soils moving out to open water with rainwater runoff or moving with the tide."

Behind the Spartina, researchers planted 6,000 black mangrove plants later in the spring of 2002. The following December they planted woody species – sweet acacia, oak, hackberry, red mulberry and wax myrtle trees – on the higher ground.

Calling the plantings "field trials," Materne said researchers are evaluating plants in relation to altered hydrology, disturbed soils and soil salts. "Not all salt is in the water," he said.

He pointed to the acacia trees that appear to be thriving on the island. This salt-tolerant tree grows to 30 feet tall and can provide habitat for migratory birds.

"We've developed engineering technology to create marsh. Now we need plant technology," Materne said. "Before we recommend that somebody spend money, we need to be sure the recommendations are good."

Rick Bogren is a writer for the LSU AgCenter.

e-mail: [email protected]

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